We have no count register in Shenandoah's arraycopy_epilogue() in jdk11/aarch64. But we're computing count a little later. We can use that instead: http://cr.openjdk.java.net/~rkennke/jdk11-fix-epilogue/webrev.00/ This unbreaks the build of sh/jdk11. Testing: hotspot_gc_shenandoah runs fine Ok? Roman